Celiac disease

What is Celiac disease?

Celiac disease is a medical condition where the body develops an abnormal reaction to gluten found in food. The abnormal reaction leads to inflammation which damages the tissue on the inner surface of the small bowel. The damage is caused by specialized immune cells called lymphocytes which are found in increased numbers in the small bowel of people with celiac disease. Another name for celiac disease is gluten-sensitive enteropathy.

The small bowel

The small bowel is a part of the digestive system. Another name for the small bowel is the small intestine. The small bowel is a long tube that starts at the stomach and ends at the colon. It is divided into three parts: duodenum, jejunum, and ileum. The duodenum is the shortest part of the small bowel. It connects to the stomach on the right side of the body just below the ribs.

Food that we eat enters the stomach where it is mixed and broken down by strong acids made by cells inside the stomach. When this is complete, the digested food moves into the small bowel. The purpose of the small bowel is to absorb nutrients from the food and transport those nutrients into the body.

The inner surface of the small bowel is lined by specialized epithelial cells that are designed to absorb nutrients from the food we eat. These specialized cells form a barrier called the epithelium. Below the epithelium is a thin layer of tissue called the lamina propria. This tissue contains many small blood vessels which support the epithelial cells.

Together, the epithelium and lamina propria form a thin layer of tissue called the mucosa. In the small bowel, the mucosa grows in a manner that creates long finger-like projections of tissue called villi. These villi allow the small bowel to have a large surface area in a relatively small space.

Below the mucosa are specialized cells that connect to form round structures called Brunner’s glands. These glands produce substances that protect the epithelial cells from the strong acid coming from the stomach.


Gluten is a small molecule that is naturally found in wheat, rye, and barely. As a result, many foods such as baked goods, pasta, noodles, cereals, sauces, and alcoholic beverages contain gluten. Gluten is normally broken down in the gastrointestinal tract into smaller parts which are then absorbed by the body.

How do pathologists make this diagnosis?

A biopsy is usually performed because the patient has symptoms suggestive of celiac disease (gluten-sensitive enteropathy), which may include weakness and diarrhea. These symptoms occur when the patient eats food that contains gluten.  Biopsies are usually taken from the 2nd part of the duodenum, where the changes associated with celiac disease are easiest to recognize.

Pathologists use the term intraepithelial lymphocytosis to describe an increased number of lymphocytes in the epithelium of the small bowel. Over time, these immune cells damage the epithelium which causes a loss of the normal villi. Pathologists describe this change as atrophy or blunting of the villi.

Your pathologist can confirm the diagnosis when they see increased intraepithelial lymphocytes in the epithelium of the small intestine, as well as the abnormal blunting or atrophy of the villi.  This blunting can further be graded as mild, moderate, or severe. In severe blunting, there are no villi seen and the epithelium looks flat.

When a tissue sample is taken from the duodenum in the early stages of the disease, the small intestine may show only mild changes including an increased number of lymphocytes in the epithelium on the inner surface of the tissue. In many early cases, the villi are still normal and the report will refer to this as no or mild villous blunting.

The finding of increased intraepithelial lymphocytes without villous blunting is not unique to celiac disease and may be seen in other conditions. For example, Helicobacter gastroenteritis, medications (ie. Olmesartan), tropical sprue, protein intolerance, bacterial overgrowth, and viral gastroenteritis all cause changes that look similar under the microscope.

A diagnosis of celiac disease (gluten-sensitive enteropathy) requires both clinical and pathological confirmation. Clinical confirmation is usually made by performing blood tests for antibodies that target tissue transglutaminase. These antibodies are found in most patients with celiac disease.

by Shaheed Hakim, MD FRCPC (updated September 13, 2021)
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